The present invention relates generally to the field of data communications and, more specifically, to controlling access of multiple ports to a crossbar resource of an interconnect device.
Existing networking and interconnect technologies have failed to keep pace with the development of computer systems, resulting in increased burdens being imposed upon data servers, application processing and enterprise computing. This problem has been exasperated by the popular success of the Internet. A number of computing technologies implemented to meet computing demands (e.g., clustering, fail-safe and 24xc3x977 availability) require increased capacity to move data between processing nodes (e.g., servers), as well as within a processing node between, for example, a Central Processing Unit (CPU) and Input/Output (I/O) devices.
With a view to meeting the above described challenges, a new interconnect technology, called the InfiniBand(trademark), has been proposed for interconnecting processing nodes and I/O nodes to form a System Area Network (SAN). This architecture has been designed to be independent of a host Operating System (OS) and processor platform. The InfiniBand(trademark) Architecture (IBA) is centered around a point-to-point, switched IP fabric whereby end node devices (e.g., inexpensive I/O devices such as a single chip SCSI or Ethernet adapter, or a complex computer system) may be interconnected utilizing a cascade of switch devices. The InfiniBand(trademark) Architecture is defined in the InfiniBand(trademark) Architecture Specification Volume 1, Release 1.0, released Oct. 24, 2000 by the InfiniBand Trade Association. The IBA supports a range of applications ranging from back plane interconnect of a single host, to complex system area networks, as illustrated in FIG. 1 (prior art). In a single host environment, each IBA switched fabric may serve as a private I/O interconnect for the host providing connectivity between a CPU and a number of I/O modules. When deployed to support a complex system area network, multiple IBA switch fabrics may be utilized to interconnect numerous hosts and various I/O units.
Within a switch fabric supporting a System Area Network, such as that shown in FIG. 1, there may be a number of devices having multiple input and output ports through which data (e.g., packets) is directed from a source to a destination. Such devices include, for example, switches, routers, repeaters and adapters (exemplary interconnect devices). Where data is processed through a device, it will be appreciated that multiple data transmission requests may compete for resources of the device. For example, where a switching device has multiple input ports and output ports coupled by a crossbar, packets received at multiple input ports of the switching device, and requiring direction to specific outputs ports of the switching device, compete for at least input, output and crossbar resources.
In order to facilitate multiple demands on device resources, an arbitration scheme is typically employed to arbitrate between competing requests for device resources. Such arbitration schemes are typically either (1) distributed arbitration schemes, whereby the arbitration process is distributed among multiple nodes, associated with respective resources, through the device or (2) centralized arbitration schemes whereby arbitration requests for all resources is handled at a central arbiter. An arbitration scheme may further employ one of a number of arbitration policies, including a round robin policy, a first-come-first-serve policy, a shortest message first policy or a priority based policy, to name but a few. The physical properties of the IBA interconnect technology have been designed to support both module-to-module (board) interconnects (e.g., computer systems that support I/O module add in slots) and chasis-to-chasis interconnects, as to provide to interconnect computer systems, external storage systems, external LAN/WAN access devices. For example, an IBA switch may be employed as interconnect technology within the chassis of a computer system to facilitate communications between devices that constitute the computer system. Similarly, an IBA switched fabric may be employed within a switch, or router, to facilitate network communications between network systems (e.g., processor nodes, storage subsystems, etc.). To this end, FIG. 1 illustrates an exemplary System Area Network (SAN), as provided in the InfiniBand Architecture Specification, showing the interconnection of processor nodes and I/O nodes utilizing the IBA switched fabric.
According to one aspect of the present invention, there is provided a method to arbitrate requests of a plurality of ports of an interconnect device. Every port receives combined pending request data that includes a pending request indicator associated with each of the plurality of ports. Each pending request indicator specifies whether a corresponding port has a pending request that needs to be submitted to a request bus of the interconnect device. Further, at each port, a turn to submit a request to the request bus is allocated to one of the plurality of ports based on the combined pending request data, a set of values stored in a mask register and a priority scheme associated with the plurality of ports.
Other features of the present invention will be apparent from the accompanying drawings and from the detailed description that follows.